This application claims the priority of Japanese Patent Application No. 2004-256859, filed Sep. 3, 2004, the content of which is incorporated entirely by reference.
1. Field of the Invention
The present invention relates to a control apparatus for a hybrid vehicle including an engine and a motor as driving sources for driving the vehicle, a power generator driven by the engine, and an electric storage device for storing regeneration energy from the power generator and the motor.
2. Description of Related Art
A hybrid vehicle has been known in which an engine that is connected to a geared or continuous variable speed automatic transmission and drives main driving wheels (i.e., the front wheels or the rear wheels) and a motor that directly drives the axle shaft via reduction gears, in which the motor is connected to a battery and is placed on the crank shaft for restarting the engine that has been stopped. In such a hybrid vehicle, by properly employing the engine and the motor according to driving conditions, a reduction in fuel consumption and emission gas are achieved.
For example, Japanese Patent No. 3099723 proposes a technique that is capable of suitably controlling an engine by running the engine when the charged capacity of an electric storage device is less than a predetermined value, or when the maximum output torque of an electric motor that is driven by driving means is less than a target torque that is calculated by calculating means.
Furthermore, Japanese Unexamined Patent Application, First Publication No. 2002-138876 proposes another technique in which respective outputs of a rotating electrical machine and an engine are determined from a ratio of the outputs according to the charged capacity of a charging element and the requested accelerator amount, and the rotating electrical machine and the engine are controlled such that the respective outputs are obtained, thereby improving the fuel consumption or the like.
In a conventional vehicle without an electric motor, deceleration energy generated during deceleration of the vehicle is wasted in a form of heat by means of a friction brake. In a hybrid vehicle, such as ones described above, in order to achieve the effect of improving the fuel consumption, it is necessary to effectively regenerate such deceleration energy using one or more motors and to use the energy for reacceleration.
Furthermore, an enhanced effect of improving the fuel consumption is generally realized when regenerated energy is used when the vehicle is driven only by the motor (motor drive mode).
However, upon transitioning from a motor drive mode in which electric power stored in a battery is used to drive the vehicle to another drive mode in which an engine is started (engine drive mode), it is necessary to determine an EV drive allowable region by allowing for electric power required for restarting the engine that has been stopped. Upon transitioning to the engine drive mode, much electric power is required to raise the number of revolutions of the engine from zero to a speed sufficient to drive the vehicle. Especially, even more electric power is required when an immediate start of the engine is requested. Therefore, when the vehicle is driven only by the motor, electric power sufficient to transition to an engine drive mode must be saved in the battery all the time, which restricts the motor only drive allowable region. As a result, even when the motor is able to output the requested driving force, a transition to the engine drive mode may occur, which hinders achieving an improvement in the fuel consumption.
Accordingly, an object of the present invention is to provide a control apparatus for a hybrid vehicle that enlarges the motor only drive allowable region while maintaining good drivability and improves the fuel consumption.